1. Field of the Invention
The present invention relates to what is called a front-opening interface mechanical standard (FIMS) system, that is, a load port apparatus, which is used for transferring, from one semiconductor processing apparatus to another semiconductor processing apparatus, wafers held in a sealed-type transport container called a pod, or for transferring the wafers from the semiconductor processing apparatus to the pot, during a semiconductor manufacturing process and the like. More particularly, the present invention relates to a load port apparatus, which has a feature in an incorporated drive mechanism for opening and closing a door.
2. Description of the Related Art
In recent years, in a general semiconductor manufacturing process, cleanliness is managed throughout the entire process by maintaining a highly clean state in only the following three spaces: inner spaces of various processing apparatuses; an inner space of a pod capable of housing wafers and transporting the wafers from one processing apparatus to another processing apparatus; and a mini-environment in which the wafers are exchanged between the pod and the respective processing apparatuses. Such a pod includes a main-unit portion which houses wafers therein and which has a wafer-insertion-and-removal opening formed in one side surface, and a lid which makes the inside of the pod serve as a sealed space by closing the opening. Further, a structure that defines the mini-environment includes an opening portion capable of facing the above-mentioned opening of the pod and a second opening portion arranged on a semiconductor processing-apparatus side so as to face the opening portion.
The load port apparatus includes a member as a partition wall provided with the opening portion, that is, a wall called a side base, a door for closing the opening portion, a door drive mechanism for controlling operation of the door, and a mount table on which the pod is to be placed. A placing base is capable of supporting the pod in such a manner as to face the opening of the pod and the opening portion each other, and brings the lid of the pod close to or separated from the door together with the pod itself. The door is capable of holding the lid of the pod. The door drive mechanism causes the door to open and close the opening portion under a state of holding the lid, and the door is caused to retract below a space between the opening portion and the second opening portion or to enter the space. A robot is arranged in the mini-environment, and the robot is capable of entering into and retracting from the inside of the pod through the opening portion and the opening of the pod, and transfers wafers between the inside of the pod and the semiconductor processing apparatus also through the second opening portion.
In semiconductor manufacturing steps, an increase in a bore diameter of wafers to be used has been promoted for higher productivity. Therefore, each of the above-mentioned pod, mini-environment, and inner space in the processing apparatus is also upsized, and accordingly there is also a demand for an enlargement of the opening portion of the load port apparatus and upsizing of the door along with the enlargement. Such upsizing of the door involves an increase in weight of the door, and further the door drive mechanism is required to have a larger actuation force according to the increased weight of the door. As a conventional door drive mechanism, there is known a structure constituted by a servomotor, a ball screw, and the like, which is disclosed in Japanese Patent Application Laid-Open No. 2004-047839.
In a case where the weight of the door or the like increases, the required drive force of the drive mechanism also increases inevitably. However, in a case where the door is directly driven by using a motor that generates such a large drive force, when there arises a problem with position control, for example, an overload is imposed on a gear or the like, and in the extreme, there is a risk that the door, the door drive mechanism, or the like is damaged. Further, in a case of the configuration in which the door abuts against the pod at the time of loading the pod, for example, highly accurate position control is required for the door or the pod in consideration of the above-mentioned overload problem. In this case, the magnitude of the drive force may be a negative factor in an attempt to increase the accuracy of the stop position of the door or the like, and therefore there is a demand to establish stop position control different from the conventional control.